Add snapshot metadata store interface
Add snapshot metadata store interface

Signed-off-by: Derek McGowan <e1c79a582b6629e6b39e9679f4bb964d25db4aa8@mcgstyle.net> (github: dmcgowan)

mikebrow/containerd,containerd/containerd,vdemeester/containerd,estesp/containerd,Wolphin-project/containerd,mikebrow/containerd,dmcgowan/containerd,estesp/containerd,kunalkushwaha/containerd,rajasec/containerd,containerd/containerd,thaJeztah/containerd,AkihiroSuda/containerd,kunalkushwaha/containerd,vdemeester/containerd,hqhq/containerd,crosbymichael/containerd,miaoyq/containerd,lichao-mobanche/containerd,yuexiao-wang/containerd,xiekeyang/containerd,chanezon/containerd,dmcgowan/containerd,miaoyq/containerd,thaJeztah/containerd,docker/containerd,crosbymichael/containerd